This invention relates in general to a method for replicating an optical element. More specifically, it concerns a method for transferring a dielectric film mirror formed on a high quality optical flat to the nonflat surface of an optical or electrooptical device, such as for example, to the silicon surface of a spatial light modulator.
A presently used method for mirror replication involves the initial step of depositing a release agent on a surface whose optical qualities are to be replicated, such as on the surface of a high quality optical flat. The release agent may be a liquid coating which is allowed to cure to a dry film of about one hundred angstroms thickness. A dielectric mirror is then formed on top of the release agent by vacuum evaporation. An optical device which requires such a dielectric mirror, but whose surface lacks the flatness properties of the replication substrate, is cemented to the prepared mirror and the cement is cured at a high temperature, such as at one hundred degrees centigrade. A subsequent abrupt exposure of the cemented assembly to room temperature provides forces of differential contraction which separate the mirror from the surface of the replication substrate. The result is a transferred mirror with an optical quality approaching that of the replicating substrate.
It has been found however, that in some applications, such as when bonding the replicated mirror to a thin silicon substrate, the heat-cure and thermal separation method described above places substantial stress on the bond and can produce distortions or even cracks in the mirror. Because of this problem, it is desirable to be able to perform the replication transfer process at room temperature, where the slow room-temperature cure of a two-component epoxy cement would minimize the aforementioned stress condition. The problem then remaining to be solved, however, is how to separate the mirror from the original substrate.